Direct observation of Cu, Zn cation disorder in Cu2ZnSnS4 solar cell absorber material using aberration corrected scanning transmission electron microscopy
Direct observation of Cu, Zn cation disorder in Cu2ZnSnS4 solar cell absorber material using aberration corrected scanning transmission electron microscopy
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DOI：
10.1002/pip.2279
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发表时间：
2014-01-01
影响因子：
6.7
通讯作者：
Durose, Ken
中科院分区：
文献类型：
--
作者：
Mendis, Budhika G.;Shannon, Mervyn D.;Durose, Ken
采用单原子柱化学分析方法测定了Cu2ZnSnS4的晶体结构和局部点缺陷化学性质。以锌富集和铜耗竭的形式，获得了纳米级组成不均匀性的直接证据。成分不均匀性的横向尺寸估计在1.5到5nm之间。光致发光证实了广泛的供体-受体过渡的存在，与观察到的阳离子紊乱一致。相对高浓度的Zn-Cu（+）对位原子给体区域局部增大静电电位并引起能带弯曲。导带的波谷和价带的波峰分别是电子和空穴的势阱。对于太阳能电池来说，这些阻止了少数载流子电子向空间电荷区边缘扩散，从而降低了载流子分离效率，也降低了大多数载流子空穴的载流子收集效率。此外，电子和空穴被困在距离很近的势阱中，重组的可能性很高，因此载流子寿命也会缩短。因此，实现高效率的太阳能电池器件需要无成分不均匀的高质量Cu2ZnSnS4晶体。版权所有：John Wiley & Sons， Ltd。
Chemical analysis of individual atom columns was carried out to determine the crystal structure and local point defect chemistry of Cu2ZnSnS4. Direct evidence for a nanoscale composition inhomogeneity, in the form of Zn enrichment and Cu depletion, was obtained. The lateral size of the composition inhomogeneity was estimated to be between similar to 1.5 and 5nm. Photoluminescence confirmed the presence of a broad donor-acceptor transition consistent with the observed cation disorder. Areas of relatively high concentration of Zn-Cu(+) antisite atom donors locally increases the electrostatic potential and gives rise to band bending. Troughs in the conduction band and peaks in the valence band are potential wells' for electrons and holes, respectively. For a solar cell, these prevent minority carrier electrons from diffusing towards the edge of the space charge region, thereby reducing the carrier separation efficiency as well as reducing the carrier collection efficiency of majority carrier holes. Furthermore, electrons and holes trapped' within potential wells in close proximity have a high probability of recombining, so that the carrier lifetime is also reduced. High quality Cu2ZnSnS4 crystals free from composition inhomogeneities are therefore required for achieving high efficiency solar cell devices. Copyright (c) 2012 John Wiley & Sons, Ltd.